Standard Electrode Potential - Definition, Cell Potential with FAQs

What is Electrode Potential?

Defining the electrode potential according to IUPAC is defined as the electromotive force that is built by the electrodes of two cells in electrochemistry. It can be represented by the letter “E”. It is impossible to calculate directly the value of single potential accurately and more precisely. By experiments it is the only method to measure the difference in potentials of two cells. While doing any experiment for calculating the value of potential one electrode is required with known potential that is termed as Reference potential and other one is unknown potential. Electrode potential depends on direction of flow of electrons, it does not depend on which electrode is working whether it is cathode or anode. It will also depend basically on three factors.

1. Electrolytic concentration

2. Pressure

3. Temperature

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Measurement of Electrode Potential:

• The measurement of electrode potential can be done when it is connected to a standard hydrogen electrode which constitutes a cell.

• The electrode which is showing negative electrode is termed as negative terminal whereas electrode which is showing positive electrode termed as positive terminal.

• The potential difference that is developed between positive and negative terminals is measured by potentiometer.

• Through Galvanometer we can identify the direction of flow of electric current outside the electric circuit.

• This helps in identifying the anode and cathode as the electrons will flow opposite to current which means in direction from anode to cathode.

• In Daniel cell,

The reaction at Anode will be an oxidation reaction i.e. loss of electrons.

Zn→Zn²⁺+2e^-

The reaction at cathode will be a reduction reaction i.e. gain of electrons.

Cu²⁺+2e^-→Cu

The net reaction will be the addition of two half reactions of cathode and anode.

Zn+Cu²⁺Zn²⁺+ Cu

Where E_cathode=0.34V, E_anode=-0.76VA

Emf of cell= E_cell=E_cathode-E_anode

E_cell=0.34--0.76

V=1.10

Cell Potential:

The measurement of cell potential can be done by the measurement of potential difference between the two half-cell in electrochemical cell. The reaction between two electrodes are redox reaction so electrons move easily. Cell potential can be measured in terms of voltage(V), which gives a certain value of cell potential.

What is standard electrode potential?

Standard electrode potential is being used for the measurement of potential at an equilibrium condition. The difference is found between electrode and electrolyte. Such a difference is called the potential of electrodes. When the concentration of all the species in a semi cell is found as unity or at equilibria condition such type of potential is called standard electrode potential.

Define Standard Electrode Potential:

In an electrochemical cell at standard terms and conditions, with pressure at 1 atm, temperature298k and concentration of the cell is 1M such type of potential is called standard electrode potential. It is symbolically represented as E°cell, which represents the standard electrode potential. It can also be defined as the half-reaction that is measured by standard hydrogen electrodes at standard conditions.

Measurement of Standard electrode potential:

While taking an example of Standard electrode potential we can determine the vale of potential using two electrodes one is hydrogen electrode and other is zinc electrode and they are connected by salt bridge and high resistance voltmeter are attached to both the electrodes. All the conditions such as temperature, pressure, concentration are kept standard to measure the standard electrode potential.

• The measurement is taken as according to reference electrodes which are standard electrodes of hydrogen. The standard electrode potential of a reference electrode (hydrogen) is 0 volts.

• The measurement of standard electrode potential can be done by pairing it with a reference electrode and checking the results of galvanic cell.

• It is to be noted that change in temperature, pressure or concentration changes the potential of the cell.

• The measurement of standard electrode potential can be done with the help of two half cells or by half-reactions that is represented below:

E^°_cell=E^°_cathode-E^°_anode

• It can be used to measure the relative strength of various reductants and oxidants.

Standard Electrodes:

When we define the electrodes which are an important component of every electrochemical cell. Standard electrodes are the point where current flows i.e. enters the electrode and leaves the electrode when it enters the electrode it is denoted as anode and when it leaves the electrode it is denoted as cathode. The electric charge is developed by the transfer of electrons from one half-cell to another half-cell. The charge is basically based on the factors of standard electrode potential with reference potential of 0 volts.

Standard Reduction Potentials:

Standard reduction potential can be defined as a species which get reduced. It can be represented in the form of reduction half reactions. Here we take an example showing you a generic element “A” and C will be the charge.

Now taking an example of standard reduction potentials where E^°=+0.340A for reaction.

Standard reduction potential for copper can be represented as follows:

Cu²⁺+2e^-→Cu

Standard Oxidation Potentials:

Standard oxidation potential is likely to be much similar with standard reduction potentials, it is the species which gets oxidised at given standard conditions. It can also be written in the form of half reaction. At standard condition general form of reaction is written below:

A(s)A^c++Ce^-

Standard oxidation potential for copper can be represented as follows:

Cu(s)Cu²⁺+2e^-

E₀^°(SOP)=-0.34V

It is to be noted that standard reduction potential and standard oxidation potential are opposite to each other in relation to sign for the same chemical species.

Relation in between standard oxidation potential (SOP) and standard reduction potential (SRP) is as follows:

E₀^°(SRP)=-E₀^°(SOP)

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Single Electrode Potential:

While defining the single electrode potential we must understand the basic requirements of electrochemical cell, and how they work. Electrochemical cell is basically consist of two half-cells, with open circuit. The two metal electrodes are placed where the ions are transferred into solution. Due to transfer of the ion single electrode will develop the potential with respect to the solution in half cell, such potential is termed as Single electrode potential.

As in the case of Daniel cell the electrodes are not connected externally so positive and negative charge develops on anode and cathode respectively. On anodeZn/Zn²⁺ negative charge will developed and on cathodeCu/Cu²⁺, positive charge will be developed so to determine the single electrode potential in such a situation an amount of charge on individual electrodes has been taken.

The single electrode potential will depend on the following factors such as:

1. Tendency of making ions

2. Temperature

3. Concentration of ions present in the solution

Half-Cell Potential:

Half-Cell Potential can be defined as potential which is developed at each individual electrode in an electrochemical cell. Overall potential can be calculated by the two-half cell in an electrochemical cell. The measurement ogf half-cell is used to help in evaluating the:

• Presence of Corrosion

• Vulnerability of the area of corrosion

The half-cell will give only the predicted probability of area prone to corrosion at given short period of time but long-term monitoring is way more necessary for prediction of severity of corrosion.

The potential difference is associated with each electrode and the magnitude of potential will depend on the nature of the individual electrode and also on the concentration of solution. The sign will depend on the direction of reaction in which it proceeds. The half-cell method is cheaper and non-destructive in order to predict the corrosion risk. Therefore, the potential of half-cell is directly proportional to the chances of occurrence of corrosion.

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